The invention relates to improvements in a jigging machine wherein a pulsation is given to a bed of minerals such as coal flowing along a horizontal surface to separate undesirable materials.
More particularly, the invention is directed to a method for generating water pulsations in a jigging machine for processing minerals, particularly coal, whereby one or more downwardly open air chambers under the jig bed are supplied with pressurized air from an air dome for lifting the jigged material from the jig bed. Air is subsequently pressed out of the chamber by lowering the water in the jig bed.
Continuous intermittent up and down jigging motion is given the mineral on the jig bed by the continual intermittent supply of pressurized air into the compartment and release of the air from the compartment. Normal operation in devices heretofore available supplied a predetermined amount of pressurized air into the chamber and then completely relieved the air from the chamber so that the water in the jig bed completely filled the air chamber between each pulsation.
The air chambers under the individual jig bed compartments are usually supplied from a common air dome. Since different water movements are required in the individual compartments, attempts have been made to achieve optimum water movements in every compartment on the basis of a control such as valves, pivoted flaps, and pivoting blades. However, even when the charging stock does not change very much in qualitative terms, such an optimization is inadequate because the separation effect is also significantly defined by the quantity on the jig bed and quantitative fluctuations of the jigging stock are unavoidable. The separating result is therefore usually unsatisfactory over a longer time and during the start-up operation as well.
Up to now, developments have been directed toward a more and more powerful and complicated jig bed control. With the assistance of air control circuits and of a freely programmable control, particularly specific start-up programs, it is fundamentally possible to individually change the opening and closing points in time for filling and emptying the air chambers given fluctuations of the charging quantity and, in particular, during start-up, this requiring highly trained personnel and raising problems of maintenance and trouble-shooting.
An object of the invention is to provide and operate a jigging machine such that fluctuations in the charging stock and fluctuations during start-up of the jigging machine remain governable. In particular, such that an "outage" of more heavily loaded compartments does not occur, such that a constrained pulsation of the water in every compartment arises and that the required operating measures no longer need be so involved that only highly trained personnel can keep the machines running through unavoidable, unexpected fluctuations and deviations. An object is to obtain self-stabilizing controls to take effect in the machine.
In terms of method, this object is achieved in that the energy of the compressed air from the air dome is first at least partially used for the compression of an air pillow in the air chamber which is constantly present. The object is achieved by a jigging machine which is characterized in that the admission and discharge of the air into and out of the air chamber occurs at such a height that a space remains when water penetrates into the chamber from below and an air cushion remains above this opening in the chamber.
Up to now, for example, a jig compartment that was overfilled threatened to fail because less and less air per pulsation period could flow from the air dome into the pulsation chamber because of the excessively loaded jig bed. The bed together with the water in the compartment offered greater and greater resistance and, when discharging the air, more and more air was displaced from the working chamber and, thus, the reserved volume became smaller and smaller. Pressure and admission time could not simply be increased because air would have otherwise have punched through into the other compartments.
What is effected by the air pillow of the invention is that the water pulsations never entirely cease or, in other words, that water pulsations can always be excited.
This operating mode is also utilized during start-up. Water proceeds into the air admission and discharge of the chambers up to a certain limited height. From air from the air dome, this relatively small water volume can always be pressed out. Air is adjacent in the upper end compartment of the air chamber. When pressurized air is admitted into the chamber, the entire water mass is not immediately placed in motion. A greater part is initially converted into compression energy since, in accord with the invention, a minimum air cushion should always remain in the air chamber. During expansion of the air, the compressed air pillow then in turn acts as a motor which presses onto the overall quantity of water in the pulsation chamber, this always being adequate in practical operation to generate jigging water pulsations.
This type of energy transmission also takes particular effect during start-up of the jigging machine. It thereby basically no longer occurs that one compartment no longer "responds" because it would require especially great quantities of energy due to an overloaded jig bed and the pressure energy from the air dome has already flowed into the compartments that were less heavily loaded during the time available, these compartments having offered less resistance to the commencement of the water motion.
It is beneficial for improving the method to additionally provide air control per compartment. That is, to adjust the fine control with the means of electronics whereby the system always remains stable. Thus, the total failure of the water pulsations is no longer possible. A defined quantity of energy is always introduced into every compartment independently of the load because of the air cushion. Of course, as hitherto, the quantity of jigging stock is an important dimensioning quantity in the design of the conduit size, the size of the air cushion and the shape of the chamber.
There have been controls wherein probes and a corresponding valve control prevented one chamber from being fully filled with jigging water, retaining a defined air cushion in the chamber, this having been generated before start-up (German Published Application No. 25 27 756). In contrast to the known "active" control susceptible to disruption, the method of the invention is an operating mode which occurs automatically, wherein at most, smaller corrections are required but wherein the desired behavior essentially occurs automatically.
It is preferred to maintain such an air cushion in the chamber and to fashion the upper region of the chamber such that the size of the cross section of the chamber is equal to the size of the air bubble, i.e., the "full" piston surface should be immediately available upon expansion. What this means for the apparatus is that the top compartment or section of the chamber is always filled with air for the full cross section and it is particularly beneficial to fashion the chamber roof as a "flat roof". The size of the air cushion is then determined by the distance of the admission and discharge opening from the top of the chamber. The distance of the opening to the top is then approximately proportional to the volume of the "air bubble" in the air chamber. In general, the bottom-pulsed jigging machine of the invention is characterized in that the admission and discharge of the air into and out of the air chamber occur at such a height that a space remains in the chamber above the air opening and air remains enclosed in this space when water enters into the chamber from below.
The characteristic of the jigging process is changed only slightly with such a jigging machine. In the method of the invention and the apparatus of the invention, there is definitely the possibility of operating the jigging machine "softer" because a pulsation can always be excited. This operating mode is especially important in the superfine grain range. Over and above this, energy savings also derive from a soft operating mode.
In accordance with the features of the invention, the energy of the compressed air supplied to the air chamber which is normally supplied from the air dome is at least partially used for a further compression of the air pillow which is present above the water level at the top of the air chamber. Thus, in the start-up condition of the jig, the movement of the water is caused by summation of the energy of the air in the air dome and the stored energy of the air pillow. It is, therefore, significant that the pulse pressure act on the entire free surface of the water column in the chamber so that a significantly larger pressure surface is located at the top of the water column in the chamber and the water column acts as a piston.
In methods heretofore available, only a small cross sectional area of the supplied air pressure acted on the water column as a working pressure surface, particularly during the start-up procedure. This disadvantage occurred in previously known jigging machines where the pulse chambers were completely filled with water at start-up. As a result of the present concept, the overall energy introduced into the air chamber operates on a larger working piston surface and the water column can be easily pushed out of the chamber for the first jigging stroke of the jig bed.
During the operating condition of the arrangement, the water column is pushed downwardly out of the chamber for the full amount of pressurized air supplied to the chamber and as a result a complex valve control is no longer required for maintaining a minimum level. Previous arrangements involved valve control because there was a risk that the water level within the chamber migrated to the extent that air blew out through the bottom of the chamber. In the present arrangement a stable water level is achieved within the chamber and the blow through of air from the chamber is avoided. With the present arrangement, the air pillow is formed above the opening into the chamber and the air pillow exercises a damping effect on the upwardly pulsing water column and stores energy in its compressed condition in order to give the water column a correspondingly high kinetic energy following the upper dead point. The downwardly directed movement of the water column is significantly accelerated by the stored energy of the air pillow and also by the energy of the compressed air from the air dome supply. The pulsating water column in the air chamber assumes the function of a valve control since the water column periodically releases and recloses the opening used for the introduction and release of the air from the chamber.
The ratio of the working area of the jigging compartment to the piston area of the water column could be chosen on the order of a preferred ratio. That is, the ratio of the working area of the jigging compartment to the piston area of the water column should be on the order of 2 to 1. In large previously known jigging machine such ratio was more on the order 3.5 to 1.
Other objects, advantages and features will become more apparent with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiment thereof in the specification, claims and drawings, in which: